Level path. The zones which most go (popular or high zem).

[DrKvothe]

10 to as high as you want, 20ish?: blackburrow for nostalgia and fangs (has it been nerfed yet?)
10 to ~16: wisps in NK/erud's crossing for exp + serious plat
~14 to 20: oasis fear kiting crocs group with pet classes
26 to ~30: OOT sisters for plat
~29 to 34: HHK goblins and/or guards

I can't stand being in the same zone for weeks. If you've got the plat for ports or some druid/wiz friends, you'll have a blast just sending tells to people within your exp level range who happen to be in zones you'd like to try. Even seriously twinked exp grinders like some company some times.